The present invention relates to techniques for detecting current changes in integrated circuits.
Advances in integrated circuit (IC) fabrication technology have greatly increased the density with which circuits can be packed on an IC chip. This has lead to a corresponding increase in the power consumption per unit area on an IC chip. In addition, increasing integration densities have allowed the operation frequency of circuits to continue to rise. As a result, circuits on an IC chip are becoming more sensitive to fluctuations in power-supply voltages. This presents a potential problem because noise in an IC chip's power supply can impair circuit behavior and performance.
Typically, power supply noise reduces the voltage between a circuit's power supply and its ground (see FIG. 1). As its power-supply voltage degrades, a circuit may slow down and become more susceptible to data corruption, because a digital circuit's switching speed generally depends on its power-supply voltage. In synchronous systems, power-supply noise local to one circuit and not to its neighbors can cause timing problems at the interface between the circuits. Moreover, power-supply noise can also cause power-supply voltage to suddenly increase. Such an increase can cause similar problems by speeding up local circuits, which can potentially introduce race-timing errors at circuit interfaces.
Power-supply noise generally arises from sudden changes in the power-supply current. Such changes may result in undesired voltage drop due to the inductance within the power-delivery system. The voltage drop ΔV can be expressed by: ΔV=L·(di/dt); where L denotes the inductance, i denotes the instantaneous power-supply current, and t denotes time. In general, one may mitigate the effects of power-supply noise by reducing the power-delivery inductance or by reducing instantaneous changes in current. However, these techniques may not suffice as the complexity and total power consumption of a chip continue to grow. Therefore, it is desirable to detect power-supply noise and to take remedial actions to alleviate the problems caused by power-supply noise.